The sea deep water well has rich oil and gas resources, as well as great potentials. As compared with the land or shallow sea drilling, the sea deep water drilling faces many special technical problems, requiring the deep water drilling fluid must have the following characteristics: (1) maintaining a stable rheological property in a “low temperature-high temperature” large temperature difference. As the water depth increases, the temperature of the sea water lowers, normally 4° C. The low temperature causes the viscosity and shearing force of the drilling fluid to greatly increase and even a distinguishing jelling effect would happen to the oil-based drilling fluid, rendering over-high equivalent circulation density, causing problems such as well leakage and difficulty in starting a pump. As the depth for drilling increases, the temperature rises gradually, and the viscosity and shearing force of the drilling fluid would lower to further cause problems such as difficulty in carrying shale. Therefore, the drilling fluid maintaining a stable rheological property in the “low temperature in the bottom of the sea-high temperature at a deep portion” large temperature difference range is crucial to the operating efficiency of the deep water drilling. (2) Effectively inhibition of borehole instability caused by hydration, expansion and dispersion of the water sensitivity shale at the deep water shallow stratum. The hydration easily happens to the water sensitivity shale when contacting water, causing borehole instability, which severely influences the smooth operation for deep water drilling. Therefore, an effective hydration inhibitor is required to be used to improve the borehole stability. (3) Effectively inhibiting a problem of congestion caused by natural gas hydrate.
The oil-based/synthesis-based drilling fluid has advantages of excellent inhibition property and high temperature stability, is a top choice for complex stratum drilling. However, the cost thereof is high and it is not friendly to the environment. The water-based drilling fluid has the advantages of low costs and friendly to the environment. However, in deep water drilling, it is hard for the conventional water-based drilling fluid to solve the problem of borehole instability of the deep-water water sensitivity shale; the rheological property is greatly influenced by the temperature, so that the pressure of the wellbore is hard to control; and the hydrate congestion risk exists, so that it is hard to meet the engineering technique requirements for deep water oil gas exploration.
Currently, for the strong inhibition water-based drilling fluid, lots of researches are developed at home and abroad. Moreover, the water-based drilling fluid that is suitable for deep water drilling and has strong inhibition property and stable rheological property at the same time needs to be studied deeply.